Lens is included in the Sunderland squad for Boxing Day’s clash at Manchester City after being dropped for last weekend’s defeat at Chelsea and made to train with the club’s Under-21s.

He was the most expensive player we bought this summer and we want to see value for money

Sam Allardyce

The 28-year-old was disciplined following an incident at the conclusion of Sunderland’s defeat against Watford seven days earlier and then conducted an interview in his native Holland this week where he admitted his frustration at the Stadium of Light and raised the possibility about leaving the club in January.

But Lens has now resumed training with the rest of the first-team squad and Allardyce has challenged the Dutch international to prove his worth after ex-head coach Dick Advocaat made him the most expensive acquisition of Sunderland’s summer spending.

Allardyce told the Echo: “He’s back in the squad to play and if he plays, he has to show us what he can do.

“He was the most expensive player we bought this summer and we want to see value for money.

“We want to see what he’s really got.

“He obviously showed that to Dick before he came to the Premier League, to encourage him to spend that kind of money.”

Lens’ sublime finish in Advocaat’s final game in charge against West Ham demonstrated the ex-winger’s undoubted quality.

But the reservation over Lens has stemmed from his work-rate, which had been a criticism during his time on the Continent with both Dynamo Kiev and PSV.

However, Allardyce acknowledges that overseas imports regularly find it difficult to adjust to the physical demands of the Premier League during their maiden season of English football.

Allardyce added: “He’s got huge talent, there’s no doubt about that, but you need talent with application at this level.